JZ-055 - Entry Node of Ring in Linked List

The entry node of the ring in the linked list

Topic description

Given a linked list, if it contains a ring, please find the entry node of the ring of the linked list, otherwise, output null.

Topic link : The entry node of the ring in the

code

import java.util.ArrayList;
import java.util.List;

/**
 * 标题：链表中环的入口结点
 * 题目描述
 * 给一个链表，若其中包含环，请找出该链表的环的入口结点，否则，输出null。
 * 题目链接：
 * https://www.nowcoder.com/practice/253d2c59ec3e4bc68da16833f79a38e4?tpId=13&&tqId=11208&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz55 {

    public ListNode entryNodeOfLoop(ListNode pHead) {
        if (pHead == null || pHead.next == null) {
            return null;
        }
        List<ListNode> nodes = new ArrayList<ListNode>();
        ListNode node = pHead;
        while (node != null) {
            if (nodes.contains(node)) {
                return node;
            } else {
                nodes.add(node);
                node = node.next;
            }
        }
        return null;
    }

    public static void main(String[] args) {
        ListNode root = new ListNode(1);
        ListNode node1 = new ListNode(2);
        ListNode node2 = new ListNode(3);
        ListNode node3 = new ListNode(4);
        ListNode node4 = new ListNode(5);

        root.next = node1;
        node1.next = node2;
        node2.next = node3;
        node3.next = node2;

        Jz55 jz55 = new Jz55();
        ListNode result = jz55.entryNodeOfLoop(root);
        System.out.println(result.val);
    }
}

[Daily Message] Life is always full of unexpected warmth and endless hope. Always look ahead at all times, and you will be invincible when you are full of hope.